The i2c-tiny-usb is a open source/open hardware project. It is meant to replace those i2c printer port interfaces often used to connect i2c sensor chips (e.g. temperature sensors) to a Linux PC. It is fully documented and based on cheap and easy to obtain hardware. It comes with a Linux kernel driver, and can thus re-use existing Linux i2c client chip drivers. It additionally comes with a libusb-based demo application that also works under Windows and Mac OS.
